Communication system



Nov; 6, 1934. R. E. MATHES .commcunon 5mm:

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V AAAAIAA III!" Alllll vvv vv llllll III!!! mvzuron R.E. MATHES BY A? ATTORNEY Alllll III" INF ||||x Nov. 6, 1934. R. E; muss COIIUNICATION SYSTEM Filed.April 13. 1952 3 Sheets-Sheet 3 INVENTOR R. E. MATH s m K [\TTRNEY Patented Nov. 6, 1934 PATENT OFFICE 1,979,484 COMMUNICATION SYSTEM menace. Mathea, Weatfleld, 1v. 1., assignor to Radio Corporation of a corporation of Delaware Application April is, 1932,8erial No.- 604.92:

14 Claim.

This invention relates to telegraph communication systems and has especial reference to a multiplex communication system.

An object of the present invention is to enable the transmission and reception of messages by radio or wire telegraph, using codes employing unequal length characters, suchas the American Morse and Continental Morse codes.

Heretofore, in signalling over multiplex telegraph circuits employing the time division method of multiplexing it has been customary to employ the constant length five unit codesystem wherein a telegraph circuit is assigned to successive channels for the entire duration of a five unit character. It is evident, however, that such method of assigning individual units of time to successive channels does not lend itself readily to systems utilizing telegraph -cod'es having unequal length characters. ,The present invention overcomes this difliculty and provides a system whereby unequal length characters can be transmitted by using a unit, hereinafter known as the channel Baud or dot-mark, as the basis of transmitting a signal of constant time duration.

A feature of the present invention resides in the electrical circuit means employed for con- 1 at the transmitting commutator.

trolling the reception of the transmitted signals. This feature increases the speed of signalling by avoiding the use of mechanical relays and dis-. tributors and the consequent inertia of mechanically moving parts. In this manner, a practically instantaneously operating, inertialess relay is obtained.

A further advantage is that the troubles inherent in mechanical contact systems such as are due to wear and tear of elements, sparking, and

structed in accordance with the principles of the present invention. Another feature of this invention is the looking circuit whose primary purpose is to fill in at the receiver the dashes of each channel omitted This circuit aids in rebuilding the dots and dashes of each individual channel into normal full length units.

This invention utilizes the dot-mark length as the basic unit of time division in the multiplex channel system. The successive units on each channel are divided into equal portions'of like number as the several channels. The outgoing transmitting circuit is, then assigned to the successive channels consecutively for a time equal to one" of these portions. The composite received signal is broken down into these same portions and each one assigned by the distributor to its respective channel equipment.

The distributor used is a multivibrator circuit designed to vibrate at a frequency slightly different from the transmitted keying speed produced by the individual channels whereby a portion of the received signal is caused to correct the phase of the multivibrator vibrations and so maintain control of the circuit. A multivibrator of this type is described in Ann. de Physique XII p. .237 (1919) .by Abraham and Bloch and is further discussed by Dr. B. Van der Pol, Jun. D. Sc., in an article on Relaxation Oscillations" appearing in the Philosophical Magazine (London) for Nov.

A better understanding of the present invention may be had by referring to the following detailed description which is accompanied by drawings in which one embodiment is illustrated diagrammatically. It is to'be distinctly understood, however, that the particular embodiment illustrated and described has been selected merely for the purpose of clearly setting forth the principles involved and that this invention is not limited in scope thereto since it may be applied to any type of general communication circuit, either wire or radio, and is susceptible of being modified to meet different conditions.

Figure 1 illustrates, diagrammatically, the transmitting apparatus used in the present invention, and

Figure 2 illustrates, graphically, the message signals in various stages of their passage to the transmitting equipment,

Figure 3 shows the receiving apparatus for one complete channel, and

Figure 4 shows, graphically, the manner in which the composite received signal is broken down and the individual message signals reconstructed.

Referring to Figure 1 in more detail, there is shown radio transmitting apparatus 1 connected to an antenna 2 and a ground 3. Means are provided (not shown) for perforating the paper tape according to the message to be sent. This may be eflected by 'any suitable perforator such as the Kleinschmidt apparatus which is well known in the art. A plurality of these tapes, corresponding in number to the number of channels in the system, are utilized to affect relay controllers (such as Wheatstone automatic tape transmitters) for actuating a circuit in accordance with the perforations in the tape. These controllers which are herein designated as 5 and 6 are driven by a common shaft 7 which is geared through reduction gears 9 to a motor 8. A commutator 11 is provided upon shaft 7 and equipped with adjustable brushes 12, 13 and 14. The controllers 5 and 6 have output circuits 15 and 16 which are connected respectively in series with the brushes 12 and 13. Other suitable means than that shown may be provided for maintaining the controllers and commutator in phase and synchronism. These might use flexible shifting from a common motor, or individual motors from a common A. C. supply.

The commutator is arranged to make one revolution for each dot cycle of the automatic transmitting controller equipment. In the present instance, since a two-channel circuit only is shown the commutator is arranged to transmit one half of a dot length of each unit of signal received from the respective controllers alternately, thus throwing away the other one half of the dot unit which is later restored by the locking circuit in the controllers from the perforated tapes.

the receiver. The composite signalling circuit 17 which actuates the transmitting equipment 1 is assigned to the successive channels 1 and 2 consecutively for a time equal to one of these one half dot portions.

Referring to Figure 2, wherein graphical representations of the transmitted signal are shown opposite their appropriate legends, the curves 1 and 2 opposite the legends channel 1 automatic transmitting controller equipment" and channel 2 automatic transmitting controller equipment represent respectively the message signals of the two channels which are produced kiln T e signal of channel 1 received at commutator 11 is broken up into two equal portions, only half of which is transmitted to the output circuit through brush 14 as shown in graph 3 opposite the legend Channel 1 Commutator. Similarly, the message signal of channel 2 is also divided into two equal portions of half dot length, only one of which is transmitted through brush 14 to transmitting equipment 1 as shown in graph 4 opposite the legend Channel 2 commutator. Since the outgoing circuit is assigned to channels 1 and 2 consecutively for a time equal to each one of these portions the combined signal will take the form indicated in the drawings as graph 5 opposite the legend Combined Signal. This combined signal is the sum of graphs 3 and 4. The signal in the antenna corresponding to this output circuit will appear as indicated by the curve 6 designated Antenna Output.

In Figure 3, which represents diagrammatically the receiving equipment, the received composite signal is first rectified by rectifier 20 and then passed on to a. coupling tube indicated, generally, by the reference character 21. This coupling tube has its output circuit connected thru a condenser 22 and an inductance 23 to a multivibrator circuit 24. Inductance 23 functions to delay the passage of a pulse therethrough to control the phasing of the multivibrator. Thus by means of a portion of the incoming signal synchronism is maintained with the transmitting commutating equipment. The grid 25 of coupling tube 21 is biased positive so that current normally flows in its anode-cathode circuit. This normally flowing current cannot affect the multivibrator 24 at this time due to the blocking eifect of condenser 22. Upon receipt of a signal, however, the coupling tube is arranged to block, thus preventing the flow of any current in its anode-cathode circuit. The steep wave front of the signal causes condenser 22 to charge rapidly, consequently transmitting a current pulse to the vibrator circuit upon each charge or discharge of the condenser.

Multivibrator circuit 24 is of a well known type used in various facsimile systems. It comprises two triode tubes connected in an interdependent circuit by means of two condensers which couple the plate of one tube to the grid of the other, and the plate of the second tube to the grid of the first. These condensers obtain a charge, alternately, through a network of resistances in the circuits external of the tubes. The voltage stored on these condensers is applied to the respective tube grids. As'described by Abraham and Bloch in the Ann. de Physique XII p. 237 (1919), the tubes act as relays, but reverse the circuit, with respect to the condensers, from charging in one direction to charging in the other direction. Pulses of current are thus transmitted at predetermined intervals over leads 37 and 36.

The vibrator circuit continues to vibrate and transmit pulses at definite intervals over leads 37 and 38 respectively, until an impulse is received from the coupling tube which controls the action of the multivibrator.

Of course, if desired, any distributor arrangement may be utilized in place of the multivibrator, such as, for example, the Gulstadt relay or a mechanically operating distributor employing a plurality of segments and a brush arrangement. It is to be understood that'if more than two channels are utilized, some other arrangement than the particular multivibrator distributor shown in the drawings will be used.

The pulses received over lead 37 from the multivibrator are impressed upon the grid circuits of tubes 26, 27 to aid in controlling the locking circuit 28. Tube 26 is normally biased considerably below cut-off so that the pulses impressed upon the grid will carry it about half way between cutoff and zero bias and cause a resulting medium amplitude current pulse to flow in its anode circuit. Tube 27, on the other hand, is biased still further below cutoff so that the pulses received over lead 37, of themselves, will not allow any current to flow in the anode circuit of this tube. This bias is obtained from battery 34 plus the IR drop in resistance 30 due to the anode current flowing in tube 29. By virtue of this difference in bias, the multivibrator pulses through tube 26, when no signals are being received, predominate over those through tube 27 and the locking circuit is thus arranged to pass current through tube 32 for spacing. Connected across a portion of the grid resistance of tube 27 is the output circuit of tube 29 whose grid is connected to the output circuit of the rectifier. The grid of tube 29 is biased positive to permit current normally to pass therethrough. When signals are received through rectifier 20, however, the bias of the grid circuit of tube 29 is changed to prevent the passage of current through this tube. a

When the signal is being received, tube 29 blocks and by virtue of the discontinuance of the IR drop through resistance 30, the bias of tube 27 is raised up to or slightly below cut-off so that if a pulse is then transmitted over lead 37 from the multivibrator the grid of tube 27 will be carried from cut-off to zero bias and will cause a resulting full amplitude current pulse to flow in its anode circuit. This pulse will be passedv to the grid of 32 at the same time that the pulse through tube 26 is passed to the grid of tube 33. However, the greater amplitude of the pulse to 32 will cause it to predominate over the pulse to 33 and will therefore cause tube 32 to block and 33'topass, vibrator pulse at thistlme is sufllcient to raise for the marking condition. The sum of resistances 30 and 31 should equal resistance 36 in order that the time constant of the grid circuits of tubes 26- and 27 should be the same.

The locking circuit comprises two electron discharge devices 32, 33 which are connected to have two conditions of electrical stability. These tubes are unstable when both are drawing current, but stable when one tube is passing current and the other blocked or prevented from doing the same. The change from one condition of stable equilibrium, such as when tube 32 is blocking and tube 33 is passing, to the other condition when tube 32 is passing and tube 33 blocking, or the reverse,

' is caused by the presence of a suitable predetermined potential in the output circuits of tubes 26 and 27. This locking circuitis more adequately described in U. 8. Patent 1,844,950 granted Feb. 16, 1932 to which reference is made for a more detailed explanation of the operation thereof.

Coupled to the output terminals of locking circuit 28- is a utilization circuit which may be any desired device, such as a relay, an ink recorder, printer or local tone oscillator. utilization circuit responds to the changes of polarity occurring in the output of 28 for marking and spacing conditions which, in turn, are due to the unbalance of the locking circuit under its two degrees of stability.

Figure 4 graphically illustrates the operation of the receiving apparatus. The received composite signal in the form of tone impulses are rectified by rectifier 20 to present a square top signal. This signal is received by coupling tube 21 which is arranged to charge. and discharge condenser 22, in turn sending impulses of different polarities to the multivibrator circuit only when the wave front of the signal output from the rectifier changes. The multivibrator distributor which normally functions to generate impulses at a natural frequency which is twice the dot frequency of the individual channel controller, is controlled by these charges and discharges of condenser 22.

Assuming, as indicated in the drawings, that at time A the rectified composite signal is positive in character the effect of the pulses through condenser 22 will be to cause the multivibrator to generate an impulse a slight interval of time later over lead 3'7. The function of inductance 23 in series with condenser 22 is to delay. slightly the action of the pulse through condenser 22 in controlling the multivibrator so that the pulse will not reach tubes 26 and 27 until the incoming signal has overcome its original transient condition and has assumed a relatively steady state at tubes 26 and 2'7.

The action of the received signals is to block the passage of current through tube 29, consequently raising the bias of the grid of tube 27 to a point at or just below cut-ofi at these blocking intervals, as indicated in the drawings by c327. The multivibrator pulse at this time will add to the voltage of c 2? due to the component now have control of the locking circuit since the This.

the potential of e 26 above cut-off while that of e 27 remains below cut-01f, consequently causing -a flow of current to the locking circuit which will reverse its degree of stability. The locking circuit will remain in this new condition until time C when the received signal, in combination with the vibrator pulse, again causes "current to flow through tube 2'7 to again control the locking circuit.

At time D e 2! is again biased above cut-off to overcome anytendency on the part of e 26 to reverse the polarity of the current applied to the looking circuit. At a time half way between D and E it will be noted that 8'27 falls considerably below cut-off. However, at this time, the locking circuit will remain in its last condition of stabflity since the vibrator pulse cannot now aifect e;26.

At time E the incoming signal' has again become positive in character and, forthis reason, 2 27 still controls the locking circuit, a condition which continues until time F.

At time F the condition of stability at the looking circuit is reversed due to the spacing condi- 'tion of the received signal and the regaining of control of the circuit by e 26. -This new condition continues up to a time between G and H when, again, the incoming signal is positive'in character. However, since there is no multivibrator' pulse at this time to drive e 27 positive the locking circuit will still remain in its last condition until time I, at which time, the action of the incoming signal, in combination with the vibrator pulse, will again cause e827 to control locking circuit 28. In this manner, tubes 26 and 2'1 are alternately under control of the incoming signal and of the multivibrator.

The output of the locking circuit 28 will produce a potential graphically represented in Figure 4 of the drawings by the curve opposite the legend "Channel #1. 'This signal, it will be noted, is identical with the signal transmitted over Channel 1 as shown in Figure 2. In a similar manner, Channel 2 of the receiving. equipas that indicated in Figure 3 of the drawings and functions in a manner identical with that of Channel 1. v

Although the present invention has been described with particular reference to a radio multiplex telegraph system, it is to be distinctly understood that it is not limited thereto since it may be applied to wire line organizations without departing from the spirit and scope thereof. Of course, in such systems, various types of associated apparatuses such as tone lines, diversity '5 receiving equipment, tone amplifiers, limiters and other auxiliary devices may be advantageously employed, if desired.

I claim: 7

1. In a multiplex, radio telegraph system, the

method of signal communication by means of codes having unequal length characters which comprises generating a plurality of message signals corresponding to the number of channels in the system, dividing the successive basic time units of the message characters of each channel into equal portions of like number as the total number of channels used, and transmitting over the ether by electromagnetic waves a composite signal formed by combining equal portions from the successive channels consecutively and discarding the remaining portions of the basic time units, subsequently receiving said electromagnetic wave composite signal, rectifying same and utilizing the rectified signal to rebuild the basic time limits of the individual message signals of each channel whereby there are effectively restored the portions of the signals which have been discarded during transmission.

'2. A receiving circuit for a multiplex, telegraph system comprising an antenna, a rectifying system coupled thereto and having an output circuit, two electron discharge devices normally biased above cut-off associated with said output circuit, said devices being arranged to become temporarily biased below cut-ofi upon the flow of signal current in said rectifying system, an impulse distributor circuit, one of said devices being arranged to control said distributor, means for reproducing the signal, said distributor and said other device being arranged to control said last means.

3. In combination, a first electron discharge device and a second electron discharge device, a common input circuit capacitively coupled to said devices and arranged to impress impulses thereon at a predetermined frequency, a common output circuit for said devices, said output circuit being under the control of that one device of the two which passes the greater amount of current, and means for influencing one of said devices in accordance with the signal currents.

4. In a receiving circuit for a multiplex telegraph system the combination with an energy collecting device and a rectifying system coupled thereto and having an output circuit, of two electron discharge devices normally biased above cutofi associated with said output circuit, said devices being arranged to become temporarily biased below cut-off upon the fiow of signal current in said rectifying system, and an impulse distributor circuit, one of said devices being arranged to control said distributor, means for reproducing the signal, said distributor and said other device being arranged to control said last means.

5. A multiplex telegraph system having a transmitting circuit and a receiving circuit, a generator circuit in said receiver functioning to generate impulses, a locking circuit for restoring the signals into their original form comprising a pair of electron discharge devices having their anodes and control electrodes resistively interconnected whereby when there is a predetermined maximum anode current in one of said devices there is a predetermined minimum current flowing in the anode circuit of the other of said devices, said generator circuit aiding to establish a reverse state of anode currents in said devices, and a utilization circuit connected to the anodes of said locking circuit.

6. In a multiplex transmission system adapted for the transmission of composite signals wherein the dot mark is utilized as the fundamental time unit, a receiving circuit comprising an energy collecting arrangement, a generator of impulses, and a signal restoring device, said signal restoring device being under control of said impulse generator and comprising a plurality of electron discharge tubes whose anodes and control electrodes are resistively interconnected, said impulse generator in turn, being under control of the incoming signals received by said energy collecting arrangement, and a utilization circuit connected to said-signal restoring device.

7. A two channel multiplex telegraph system .wherein the dot mark of the individual channel is used as the fundamental time unit having in combination a generative multivibrator circuit, a first electron discharge device and a second electron discharge device, a common input circuit for said two devices coupled to said multivibrator circuit, said multivibrator circuit being arranged to impress impulses of a desired polarity on said common input circuit at 'a natural frequency equal to the dot frequency, a common output circuit for said devices, said output circuit being under the control of that one device of the two which passes the greater amount of current.

8. A multiplex telegraph system wherein the dot mark of the individualchannel is used as the fundamental time unit, having a transmitting circuit and a receiving circuit, a multivibrator in said receiving circuit functioning to generate impulses of a desired polarity at a natural frequency equal to the dot frequency, and a circuit including a serially connected condenser and inductance coupled to said multivibrator for maintaining its synchronism with the transmitting circuit.

9. In combination, a first electron discharge de vice, and a second electron discharge device, a common input circuit coupled to said devices and arranged to impress impulses thereon at a predetermined frequency, a common output circuit for said devices, said output circuit being under control of that one device of the two which passes the greater amount of current, a signal receiving circuit, and a connection from said signal receiving circuit to one of said devices for influencing said one device in accordance with received signal currents.

10. In combination, a first electron discharge device, and a second electron discharge device, a common input circuit coupled to said devices and arranged to impress impulses thereon at a predetermined frequency, a common output circuit for said devices, said output circuit being under control of that one device of the two which passes the greater amount of current, a signal receiving circuit, and a connection from said signal receiving circuit to one of said devices for influencing said one device inaccordance with received signal currents, said connection including an electron discharge device normally biased above cut off, but which is arranged to become temporarily biased below cut off upon the flow of signal current in said signal receiving circuit.

11. A system as defined in claim 10 characterized in this, that said common input circuit comprises a multivibrator circuit.

12. In combination, a first electron discharge device, and a second electron discharge device, a common input circuit coupled to said devices and arranged to impress impulses thereon at a predetermined frequency, a common output circuit for said devices, said output circuit being under control of that one device of the two which passes the greater amount of current, a signal receiving circuit, and a connection from said signal receiving, circuit to one of said devices for influencing said one device in accordance with received signal currents, said common output circuit comprising a pair of electron discharge devices having their anodes and control electrodes resistively interconnected whereby when there is a predetermined maximum anode current in one of said devices there is a predetermined minimum current in 'the anode circuit of the other of said devices, said signal receiving circuit and common input circuit functioning to establish a reverse state of anode currents in said devices.

13. In combination, two electron discharge devices, means for normally biasing said two devices difierently below cut-01f, a common input circuit for said devices comprising a generator of pulses, one of said devices being arranged to become temporarily biased above cut-oft upon the occurrence of said pulses in said input circuit,

a signal receiving circuit, and a connection from said signal receiving circuit to said other device, said other device being arranged to pass current only under the simultaneous influence of said generator of pulses and said receiving circuit.

14. A multi-channel multiplex telegraph sysing a predetermined relationship with respect to the dot frequency, and means at the receiving circuit responsive to the signals received for maintaining the generator in synchronism with the transmitting circuit.

' RICHARD E. MATHES. 

